had done to assess problems like these – noting the effect of the filler, resin, additives and die geometry. All experiments were carried out in a twin-screw extruder, and a capillary rheometer was used for further characterisation. When running materials containing either rice

Above: WPCs are commonly used in

decking in place of traditional wood products

“At the moment, it’s too expensive,” he said. “Maybe that’s one reason why WPC windows have not been successful.” Several companies have launched WPC-based window products, including Switzerland-based Fentech, with its Fibrex product. However, the product did not gain a significant share of the market, said Friedrich. Other than trying to reduce the price of WPC window frames, more research is needed into improving surface appearance, flame retardancy and recyclability, said Friedrich. “WPC products are coming to the end of their lives – and recycling them is a problem that is very close,” he said. “Nothing will happen unless there is pressure. It’s currently hard to know how recyclable it is compared to pure PVC.” Other conference delegates brought up potential problems of WPC-based window frames, such as weldability. “There would be far more applications of WPCs

if production costs were lower,” he said. “We have had many ideas for WPC products – not just window frames – but many of them are not economical.” At the moment, he said that the economic advantage that WPC would bring – by saving on heating costs – are not outweighed by the higher price of using the material.

Processing aids

Despite the many advantages of WPCs – such as moisture resistance and easy installation – they can be difficult to process. At the Profiles USA confer- ence earlier this year, Ali Goger, research engineer at Ingenia Polymers of Canada, told delegates how the company had assessed the effect of different elements in the formulation on product quality. Processing aids are needed to overcome issues such as edge tearing, weak mechanical properties, narrow processing windows and poor flow properties. He presented details of tests that the company

14 PIPE & PROFILE EXTRUSION | November/December 2019

husks or sawdust – at loadings of 50% and 60% – Ingenia found that increasing shear rate and wood content helped surface stability in both cases, which heled to reduce edge tearing. For the resin itself, the company found that those with lower melt index put higher stress on the material – leading to better surface stability. The company also tested a number of lubricant

packages – including multi-stearates and its own formulations – at loadings ranging from 1% to 4%. It found that multi-stearate systems had an antago- nistic effect on surface stability. With its own proprietary lubricant systems, it said edge tearing could be removed at loadings as low as 2%. In future, the company plans to develop new

compatibiliser systems to improve physical properties when recycled polymers are used. Other additives will boost adhesion between the WPC core and capstock material, raise flame resistance and reduce water uptake.

WPC additives Struktol highlighted a number of additives for wood-plastic composites during K2019 – including lubricants, coupling agents and capstocks. TPW 813 is a coupling agent that claims to offer superior properties compared to traditional products. As well as providing good flexural

properties, it is effective in reducing water absorp- tion, resulting in a more durable product that can withstand many more wetting and freeze-thaw cycles. The additive can be used with any type of lubricant – especially Struktol’s TPW 617 lubricant/ process aid. Struktol’s products for WPC decking includes

TPW 420, a full capstock compound that offers high durability, scratch resistance, adhesion to substrate and processability, with a low gloss surface. In addition, its TPW 230 – a masterbatch version of TPW 420 – is designed to be let down with polyethylene resin. To further expand the capstock line, Struktol is developing a new line of compounds with a ‘soft feel’ surface. These compounds offer superior anti-slip properties with an increased coefficient of friction. The focus of these new compounds will be handrails, poolside decking, stairs, ramps and any other applications where a softer surface with better grip and feel is required. They can be

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